Embodiments described herein relate generally to direct tension indicating apparatus, and more particularly, to a direct tension indicating apparatus including a direct tension indicating washer and a base washer.
Direct tension indicating washers are used to indicate when proper bolt tension has been reached. U.S. Pat. No. 5,931,618, the entire contents of which are incorporated herein by reference, discloses an exemplary direct tension indicating washer. FIG. 1 is a top view of the direct tension indicating washer from U.S. Pat. No. 5,931,618. FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1. Direct tension indicating washer 60 includes protuberances 12 formed on a first surface 14 and corresponding indentations 16 formed on a second surface 18. The direct tension indicating washer 60 includes channels 62 in bottom surface 18 that lead from each indentation 16 to the outer diameter of the direct tension indicating washer 60. The indentation 16 is filled with an indicating material 64. When direct tension indicating washer 60 is used with a bolt, protuberances 12 are compressed as the bolt is tensioned. When the desired bolt tension is achieved, indicating material 64 emerges from channel 62 at the outer diameter of direct tension indicating washer 60. The emission of the indicating material provides a visual indicator that the bolt has been properly tensioned.
In some installation environments, the installation surface adjacent to the second surface 18 may be rough, worn, pocked, etc. For example, a mounting flange for joining two pipes may have an irregular surface due to the lack for any tolerance control on the surface and/or repeated assembly/disassembly of the pipes. When the direct tension indicating washer 60 is used on such a surface, the indicating material may become smudged or smeared, rather than emit cleanly from the outer diameter of the direct tension indicating washer 60.